Art of sizing paper



Patented N... 8, ma

UNITED STATES ART OF SIZING PAPER Gerould '1. Lane and Ralph W. Peters, Rochester,

N. Y., assignors, by mesne assignments, to Eastman Kodak Company, Jersey City, N. 1., a corporation of New Jersey No Drawing. Application April 14, 1986, Serial No. 74,343

13 Claims.

This invention relates to improvements in the art of sizing and more particularly to the sizing of paper.

It has been common practice to size paper with materials such as soaps, animal glue, wax, rosin and starch, in order to improve the quality of the paper as regards its water resistance, strength, writing quality, age resistance, etc. While'such treatment eflects improvement in some properties of the paper, it has left much to be desired, especially as regards water and age resistance, as well as strength. Rosin is commonly used as a beater size, but it has the disadvantage of decreasing the age resistance of the paper and does not impart sufllcient water resistance. Soaps, glue and starch do not materially increase the water resistance of the paper and result in only slight increase in strength. It is necessary that photographic paper have a high wet strength and excellent age resistance and the sizes of our invention yield improved paper for use in this field or other arts where such qualities are of importance.

In beater sizing, it has been customary to add the size to the suspension of pulp in the beater in the form of solutions in organic solvents, or as emulsions. Such practice has been necessary in order to obtain a uniform distribution of size throughout the pulp fibers. This practice is disadvantageous, since undesirable foreign solvents are introduced into the pulp and, in cases where emulsions are used, the general result is rapid breaking of the emulsion with separation of large lobules of the size and resultant uneven distribution.

It is an object of this invention to provide improved processes for sizing fibrous sheets and particularly for sizing paper. Another object is to provide a process for producing sized paper having a high tear and wet strength and excellent aging properties. A still further object is to provide an improved paper product. Another object is to provide a process for producing sized paper excellently suited for photographic purposes. A further object is to provide a process for beater sizing of paper which avoids the necessity of using emulsions or introducing foreign solvents into the pulp. Other objects will appear hereinafter.

These objects are accomplished by this invention which, in its broader aspects, comprises treating paper pulp before it is formed into sheets with certain vinyl resins, such as the water-soluble type produced by reaction of an aliphatic aldehyde with a polyvinyl alcohol. In the preferred embodiment, a cold water-soluble resin of this type is employed.

In the following examples and description, we have set forth several oi. the preferred embodiments of our invention, but it is to be understood that they are included for the purpose ofillustration andnot as a limitation thereof.

It has been found that paper of high quality can be obtained by sizing paper pulp prior to sheet formation, and preferably while in suspension in the pulp beater, with a water-soluble vinyl acetal resin. Since the resin is soluble in water, it can be added to the pulp in aqueous solution, thus avoiding contamination of the pulp with foreign materials. The resin can be dissolved in water and added to the pulp at any stage in the beating operation and in any convenient manner, such as by jetting.

Suitable water-soluble vinyl acetal resins can be produced by reacting an aliphatic aldehyde such as formaldehyde, acetaldehyde, etc. with a polyvinyl alcohol, the proportion of aldehyde used being insuilicient to completely react with the hydroxyl groups, resulting in a polyvinyl acetal which is soluble in water. The polyvinyl alcohol is produced by methods well known in the art, such as by hydrolysis of a polyvinyl ester, such as polyvinyl acetate or'propionate. The aldehyde can be added to the saponification mixture after the hydrolysis has been completed, but it is preferred to add the aldehyde to the reaction mixture and have it present during the'hydrolysis, so that the polyvinyl alcohol reacts with the aidehyde as it is formed. Although a completely hydrolyzed,polyvinyl ester or substantially pure polyvinyl alcohol can be used to combine with the aldehyde, it is sometimes desirable to hydrolyze incompletely sothat some of the polyvinyl ester is present in the final product.

Polyvinyl acetal resins having substantial solubility in cold water, such as at below 10 C. are obtained by employing amounts of aldehyde suflicient to give above about 50% acetal content, but insufficient to react with all hydroxy groups present in the polyvinyl alcohol. With formaldehyle and acetaldehyde, cold water solubility at below 4-5 C. is obtained, if at least 13% and preferably above 15% of uncombined hydroxyl calculated as polyvinyl alcohol is present in the final product. With higher aldehydes, such as propionaldehyde and butyraldehyde, the uncombined hydroxyl should be above 20 to 30%. The remainder may be polyvinyl esters. By increasing the hydroxyl content materially above the limits set forth above and decreasing the amount of acetal and ester present, the temperature at which the resin dissolves in water can be raised. Since the cold water-soluble resins have better sizing properties and yield a more water resistant and stronger paper, it is preferable to employ resins of this type.

The resin is added to the paper pulp in aqueous solution of any desired concentration. As the aqueous solutions are viscous, in the concentrated state, it is best to dilute with at least 4 volumes of water. Although it is desirable to employ only water as a solvent, water-soluble solvents, such as alcohol, may be present in addition to the water, without materially aflecting the characteristics of the paper. The proportions of resin added to the pulp depends upon the application to which the paper is intended. General, proportions of up to 10% resin based on the dry pulp are satisfactory for all usual purposes. Most practical amounts are generally between .01 and 5%. Amounts of between .05 and 2% have been found to be most satisfactory in sizing paper to be used for photographic purposes.

The resin can be added to the pulp in the beater at any stage of the beating operation. It is desirable to add the size after the pulp is nearly ready to be formed into the sheet and the beating continued for a period of time suflicient to completely disperse and intimately mix the size with the pulp fibers. On forming the pulp into a web in known manner, the resin will be intimately mixed with the cellulose fibers and will fuse or become tacky on application of heat, such as in the drying operation and thus cement the fibers together. The use of the water-soluble resin enables complete dispersion of the size throughout the pulp to yield a uniformly sized paper. Also, due to the characteristics of the resins employed, a sized paper of remarkably high tear, Mullen, wet strength and penetration resistance is obtained.

When employing a vinyl resin which is watersoluble at ordinary temperatures, no precipitation will take place on addition to the pulp. This fact results in perfect distribution of size throughout the pulp fibers. When using the cold watersoluble variety, it will be found that precipitation of resin takes place soon after addition to the beater. However, as the resin is slowly precipitated and is somewhat soluble, substantially perfect dispersion is obtained before complete precipitation has taken place. Disperson is assisted by slow addition or by introduction at a number of places. If desired, it is possible to employ a cooled or chilled suspension of pulp, so that the cold water-soluble variety can be added without any tendency to precipitate. After complete dispersion, the resin can be thrown out of solution by warming either in the beater or on the web, as a result of the temperature of the atmosphere.

The pulp containing the solution or suspension of resin is formed into paper sheets in any manner well known in the art. Heat applied during the drying or finishing of paper, such as in the drying rolls, fuse the particles or coating of size so that the paper fibers are uniformly cemented together. Since paper is rarely treated with water at a temperature below 5 C. it is usually unnecessary to harden the cold water soluble resins by heat treatment, it being merely necessary to heat them at a temperature and for a period of time sufficient to fuse and cement the sizing particles. However, both water soluble types of resins can be thermally hardened into a water insoluble form by heating for a period of time which varies according to the temperature used. Any temperature above the fusing point may be used for this purpose, but it is preferred to employ temperatures above C. such as between 200" and 300 C. in order to shorten the time required. Although it is convenient to employ the drying rolls as a means for fusing and thermally hardening the size, the thermal treatment can be applied in any other convenient manner or place in the paper making operation, such as at the calendar rolls, or after the paper has been removed from the mill.

Example I.--52 lbs. 2 oz. of a polyvinyl acetate resin, known by the tradename Gelva" was placed in a stainless steel tumbler and dissolved in a mixture of 41 lbs. 5 oz. of ethyl acetate and 54 lbs. 10 oz. of ethyl alcohol. When completely dissolved, there was added 13 lbs. 5 oz. of paraldehyde and 2 lbs. 5 oz. of paraformaldehyde; after cooling to 30 C. there was added with stirring, a catalyst mixture of 1656 cc. of sulfuric acid in 3493 cc. of water. The reaction mixture was tumbled at 70 C. for 7 hours, cooled, diluted with acetone to suitable viscosity, and precipitated by pouring into 150 gallons of water. After washing free of solvents and acid, the suspension of resin in 150 gallons of water was chilled to below 4 C. at which temperature it dissolved. 25 gallons of this solution, containing about 5 lbs. of resin, was slowly Jetted into a water suspension of 800 lbs. of dry pulp in a paper beater. The resin produced in this manner was found on analysis to contain 7.3% polyvinyl acetate and 15.4% polyvinyl alcohol. The suspension of resin and pulp was formed into a paper sheet in conventional manner. On application of heat at the drying rolls, the size fused at 104 0., resulting in a paper having high tear and wet strength, excellently suited for photographic uses.

Example II.-10 lbs. of Gelva" was dissolved in a mixture of 20 lbs. of ethyl acetate and 10 lbs. of ethyl alcohol. 2.5 lbs. of paraldehyde was added and the solution cooled to about 30 C. A mixture of 1 lb. of sulfuric acid and 1 lb. of water was then added with stirring. The mixture was agitated for six days at 40 C., cooled, precipitated and washed in the manner described in Example I. The wet precipitate from the washing operation was added to 30 gallons of water and the suspension chilled to 0 C. and stirred until dissolved. The solution thus produced containing about 5.2 lbs. of resin was added to a water suspension of pulp in a paper beater which had been stocked with 400 lbs. of dry pulp. The resin produced in this example had a polyvinyl alcohol content of approximately 15.1%.

- Example III.In a glass-lined l0-gallon tumbler, 10 lbs. of Gelva was dissolved in a mixture of 20 lbs. of ethyl acetate and 10 lbs. of ethyl alcohol. To this solution was added 1.8 lbs. of paraformaldehyde. After thorough mixing and cooling to 30 C. there was added a catalyst mixture of 1 lb. of sulfuric acid in 1 lb. of water. The reaction mixture was then tumbled at 40 C. for 6 days. At the end of this time, the solution from the reaction chamber was diluted with acetone and precipitated by slowly pouring into about 30 gallons of water vigorously agitated by a high speed stirrer. After thorough washing with water, the wet precipitate was mixed with 15 gallons of water and chilled to below 4 C. The solution thus obtained was added to a paper beater containing 400 lbs. of pulp based on the dry state. The pulp-size mixture was formed into paper sheets on a conventional paper makingmachine. Fusing and hardening of the size resulted on passing over rolls heated to C.

It is apparent that the size can be added to the suspension of pulp in other places than the beater, such as in the jordan or any place in its travel from the beater to the foraminous wire and we include, as within the scope of our invention, the addition of the size to the paper pulp at any stage prior to that at which it is formed into a sheet.

An advantage of this invention is that paper sheets of high quality as regards Wet and dry strength and permanence, such as required in the photographic industry, can be readily and economically produced. Another advantage of this invention is the elimination of unequal sizing or spotted sheets commonly obtained when size emulsions are used. An outstanding advantage 'is that paper produced in accordance with my invention does not affect light sensitive emulsions employed in coating photographic paper and is unaffected byv alkaline and acidic developing and fixing baths.

What we claim is:

1. The process which comprises treating pulp before formation into a paper sheet with a vinyl gliphatic acetal resin soluble in water at below 2. In a process of sizing paper, the step which comprises adding to the pulp before formation into a paper sheet, a cc'ld-water-soluble vinyl acetal resin produced by reacting a low molecular weight aliphatic aldehyde with a polyvinyl alcohol, the aldehyde being used in amounts insufficient to combine with 'all hydroxy groups present.

3. In a process of sizing paper, the step which comprises adding to the pulp before formation into a paper sheet, a cold-water-soluble vinyl acetal resin produced by reacting a low molecular weight aliphatic aldehyde with a polyvinyl alcohol, the aldehyde being used in amounts sufficient to give at least 50% vinyl acetal and leave at least 13% uncombined hydroxyl calculated as polyvinyl alcohol.

4. In a process of sizing paper, the step which comprises adding to the pulp before formation into a paper sheet, a cold-water-soluble vinyl acetal resin produced by reacting a low molecular weight aliphatic aldehyde with a polyvinyl alcohol produced by hydrolysis of a polyvinyl ester, the aldehyde being used in amounts sufficient to give at least 50% vinyl acetal and leave at least 15% uncombined hydroxyl calculated as polyvinyl alcohol.

5. In a process of sizing paper, the step which comprises adding to the pulp before formation into a paper sheet, a cold-water-soluble vinyl acetal resin produced by reacting formaldehyde with a polyvinyl alcohol, the aldehyde being used in amounts insufficient to combine with all hydroxy groups present.

6. In a process of sizing paper the step which comprises adding to the pulp before formation into a paper sheet, a cold-water-soluble vinyl acetal resin produced by reacting acetaldehyde with a polyvinyl alcohol, the aldehyde being used in amounts insufiicient to combine with all hydroxy groups present.

'7. In a process of sizing paper, the step which comprises adding to the pulp before formation into a paper sheet a cold-water-soluble vinyl acetal resin produced by reacting a mixture of formaldehyde and acetaldehyde with a polyvinyl alcohol, the aldehydes being used in amounts insuificient to combine with all hydroxy groups present.

8. The process of sizing paper which comprises adding to the pulp in a paper beater up to 10% by weight, based on the dry weight of the pulp, of a cold water-soluble vinyl resin obtained by reacting a. low molecular weight aliphatic aldehyde with a polyvinyl alcohol, the aldehyde being employed in amounts suflicient to give at least 50% acetal, but leave at least 15% uncombined hydroxyl calculated as polyvinyl alcohol.

9. In a process of sizing paper which comprises adding to the pulp in a paper beater between .05 and 2% by weight, based on the dry weight of the pulp, of a cold-water-soluble vinyl resin obtained by reacting formaldehyde with a polyvinyl alcohol, the aldehyde being employed in amounts sufficient to give at least 50% acetal, but leave at least 15% uncombined hydroxyl calculated as polyvinyl alcohol.

10. In a process of sizing paper which comprises adding to the pulp in a paper beater between .05 and 2% by weight, based on the dry weight of the pulp, of a cold-water-soluble vinyl resin obtained by reacting acetaldehyde with a polyvinyl alcohol, the aldehyde being employed in amounts sufficient to give at least 50% acetal, but leave at least 15% uncombined hydroxyl cal culated as polyvinyl alcohol.

11. The process of sizing paper which comprises adding to the pulp in a paperbeater between .05 and 2% by weight based on the dry weight of the pulp of a cold-water-soluble vinyl resin obtained by reacting a mixture of formaldehyde and acetaldehydewith a polyvinyl alcohol, the aldehydes being employed in amounts sufllcient to give at least 50%acetal but leave at least 15% uncombined hydroxyl calculated as polyvinyl alcohol. f

12. As a new article of manufacture, paper of improved quality containing as a size a coldwater-soluble vinyl aliphatic acetal resin which has been fused by application of heat.

13. As a new article of manufacture, paper of improved quality containing as a size a resin produced by reacting a polyvinyl alcohol with a low molecular weight aliphatic aldehyde, the aldehyde being reacted in amounts sufficient to give at least 50% vinyl acetal but leave at least 15% unreacted hydroxyl calculated as polyvinyl alcohol.

GEROULD T. LANE. RALPH W. PETERS. 

